1. Field of the Invention
The present invention relates to a wireless communication system.
2. Background Art
Conventionally, there is known an order entry system where in an eating establishment such as a restaurant, serving staff holds a handy terminal to input order information and dishes ready to be served is notified to the serving staff through the handy terminal.
An order entry system includes at least one handy terminal, a controller and a printer. Each of the serving staff holds one handy terminal, and order information regarding an order from a customer is input in the handy terminal. The input order information is transmitted from the handy terminal to the controller by wireless communication and is printed by the printer. The cooking staff confirms the printed order information by sight and performs the cooking.
There are some order entry systems which use specified low power radio (430 [MHz]) as wireless communication between a plurality of handy terminals and the controller. With such order entry system, stable communication can be obtained. However, since the baud rate is low and the carrier occupying time is long, when a plurality of handy terminals is used simultaneously, the radio collision rate rises and congestion occurs.
As a wireless communication method of an order entry system to avoid congestion, there is known CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance). In the CSMA/CA method, when a handy terminal transmits data to a controller, carrier sense is performed and when the wireless channel is in an idle state, frame transmission is performed. Then, after back off time passes, the handy terminal performs carrier sense for the next frame transmission and after transmission deferring time passes, the handy terminal transmits the next frame to the controller.
In an order entry system which performs wireless communication in the CSMA/CA method, there is known a configuration which sets the back off time increased according to the number of handy terminals (for example, see Japanese Patent No. 3970563). Moreover, in an order entry system which performs wireless communication in the CSMA/CA method, there is known a configuration which sets the back off time, in which a condition window CW and a random number are multiplied, increased according to the number of terminals (for example, see Japanese Patent No. 3762422).
In an order entry system including a plurality of handy terminals, the number of packets of communication by each handy terminal may be unbalanced. For example, when there is an unbalance in the number of orders in each area of the establishment handled by each serving staff, the number of packets of order information is also unbalanced. However, in a conventional order area system which performs wireless communication in the CSMA/CA method, the number of packets of each handy terminal is not considered. Therefore, the handy terminal with a large number of packets is provided with the same opportunity of communication as the handy terminal with a small number of packets, and communication efficiency may become bad.